Glass-to-metal seal



Patented Jan. 8 1946 y I GLASS-TO-METAL SEAL Robert H. Dalton, coming, N. 1., assignor to" Corning Glass Company, Corning, N. Y a cor notation of New York- Application March 2, 1943, Serial No. 477,735

40mins. (c1. 106-54) This invention relates to glass-to-metal seals and particularly to hermetic glass seals with metals such as molybdenum and the alloys of iron,-

nickel and cobalt, an example of which is the alloy known as Fernicofiand comprising 54% Fe, 28% Ni and 18% Co. It has heretofore been shown that such alloys are particularly suitable for sealing with certain known hard borosilicate glasses because, with respect to their expansion characteristics, these alloys more nearly resemble the glasses than do the low expansion metals, tungsten and molyb- "denum, which had up until then been used for sealing with borosilicate glasses. 1

In making a hermetic seal betweenthese alloys and glass for electrical purposes, it not only is essential that the expansion characteristics of the metal and the glass be 'sufllciently well matched,

but it is equally desirable that the glass have the highest possible chemical durability and electrical resistivity, coupled with a working temperature suificiently low to avoid over-oxidation or melting or the metal when heated to glass welding temperatures, and a melting temperature sufficiently low to permit production or the glass in conventional melting units. 'It is also desirable that the expansion and viscosity be such that the glass is capable of sealing both to Fernico and to molybdenum. s

The prior glasses used Iorsealing with the above mentioned alloys have not been entirely satisfacalloysor-iron, nickel and cobalt'are given for tory in all these respects and, although any and all 01' the desirable qualifications may be obtained at the sacrifice of others, heretofore no single lass has combined them all.

An object of this invention is to provide a glassto-metal seal which is suitable for electrical purposes at elevated temperatures.

Another object is to produce a glass suitable for such a seal and having ,a higher electrical resistivity at 350 C. and a better chemical durability than prior sealing glasses.

Another object is to produce a glass which will seal with an alloy of iron nickel and cobalt and which will have a higher electrical resistivity at 350 C. and abetter chemical durability than prior sealing glasses used for this purpose.

. Another object is to provide a glass which will seal with Femico and also with molybdenum.

To'these and other ends the invention includes taining silica, 'borlc oxide, alumina and alkali comparison.

Table I- a A B O D Si0| 67.4 66.9 67.6 -66. B 0; l5. 4 15. 1 15. 2 15. 8 A110," 7. i5 7. 4 7. 4 .7.4 Nai0.- 1.4 .7 2.7 2.5 0..- 3.5 4.6 2.3 2.9 Li O.-. .8 .8 .8 .8 CBFL- 3.0 B80... .4 2.8 8.0 2.8 KG! -1.o 1.0 'i .o 1.0 Electrical rosistivitg in megohms per cm. cube 350 18.41 35.08 9.33 11.80 Settin point 13?... 0.- 400 .467 459 461 Chem caldurab ty'..- 2.3 2.3 1.0 1.

Table II E I l" G Si0|. 66.5 68.5 15.0..-. w p 20.5 23.0 24 A1103..." 6.0 2.0 a N820 8.0 AGJ 0 .Electrical resistivity in megohms per cm. cube 7 at 350" 0 1.32 6.89 2.67. Betting point termienturo 495' 476 474 fChemical durab ty 3.3 Q 11 10-20%, A: 640% and the alkali metal oxides comprising not over 5% K20 and not over 2% L120, with or without'but not exceeding 3% NaaO, are particularly suitable forsealing with the Fe.

Ni and Co alloys and with molybdenum and have a high electrical resistivity'and a better chemical durability than prior glasses used for this purpose. The glasses may also contain 38.0 or CaFz in small amounts but these and other additional con-f stituents should preferably not exceed about 10-15% of the total composition. Chemical durability is deflned as the loss in' weight in milligrams'per sq. cm. which the glass undergoes during immersion for twenty-four hours in a boiling fiftieth-normalsolution of sodium carbonate as compared with that of a known glass. The chemical'durability is herein expressed as the ratio between the amount lost by the sample and-the amount lost under the same conditions by astandard glass or high durability, and the lower the ratio the better the durability.

In Table I preferred examplesof my new com-'- I positions falling within the scope of this invention are given in terms oi weight per cent as calcu-..

lated from their respective batches, and in .Table 11 some of theprior glasses used for sealing with As a source of lithia I have preferably used metal oxides. the 810: being 60-75%, B20! is lepidolite in classes A. 3.1:. and D because it is cheaper than refined lithium materials and it contains. as other desirable constituents, alumina,

soda. potash, and a small amount of fluorine.

factory for my purpose and which are substani-l tially free from soda may also be made i! a sodafree source of lithia is used. This would have the disadvantage of greatly increasing the cost of the glass.

The above recited compositions, being calculated from their respective batches, are ,not exactly the compositions of the final glasses there is a small indeterminate loss during melting. However, the difference is not substantial alt-iis'zshmavis mule -hycomparing;- the- 031icflutedconmositimuofgldssD-wfihthat obtained.

which; was as ioiiowst; Sins... 1.511%; B103, 7.4%-

(116%:11120, 2.6% NazQ.

'- 3-.%.-K20, 036%" man-coma; C1. 3 noted that-218$ D also containsbm analysis aa'small. amount oi: fluorine. derived; irom the lspidolite whichwas usedas a-batch material. The fluorine contents areinotstated in: the: calculated compositionsfor the .new glasses A. B. (2.. soil); becausesof the uncertainty asto the quane my present and the form in which it is retained expansion and temperature for these metals and the new glasses, reference is had to the drawing which shows the so-called expansion curves obtained by plotting the specific elongation.

where his lengttu-againsttsmporatuns for molybdenum, E'emiod and glass C of Tibial. It will be seen that the three curves intersect both at 1 ;room temperature and at 460 C. and that at this temperature AL E 182890: Since the-setting point of glass is 459 6:, this glass-will form successful hermetic seals with bothof; these metals. Practically it is not necessary that the setting point of the glass be exactly 460 C. and a small variation is permissib1e.. Howeyer exoeptior very the variation in settingr temperature of. the.

glassifrom 4.60? C. shouldnohbe-largeenoflzh to. I I

about 100.. 'meseeonditionsoan roadily be deter-- inzthe'flnalglass. but thereis: no doubt that,.like- I glass D, thelother. glassesxA, B, and C alsocontain fluorine, the-amounts of: which can be determined.

1 bysnaiysisa Thepresenoe- -of. asmall amount of fluorine; whether derived from lspidolite or other fluorine-containing. material; is believed to be desirable because it.- has a substantial. influencein=. softening the g-lassandraisingv the chemicaldurability and electrical resistivitythereof.

The chemical and electrical resistivityzof the new giasses A..B-. C, and D are hi herthmithose of= the priorglasses E..F,. and G-. It isthither-noted that-the setting; point temperature;

mined byymessunement.- The ability of. the new. glasses tOqSBaa' both; to Femicoj' audits-mow dsnuxn. is advantageous because 'asingle glass: can-now-be usedwhere two would otherwise beret-- quired and the saving in melting facilities. and.

as timeand r'naterialsis thus clearly apparent.

lolaimz.

1. a glas oft high. electrical. 'resistivitame I chemical.durabilityconsists of approxie 40 A1203. 11-3-%. Wit-5% K20,

oi the new glasses. A, B,. C. and D. are close to.

460? C. By setflingrpoint; temperature. as used:

herein, is meant the temperature belowwhiohtheglass has insuflicient plsfliie'flow to relieve strains setup in the glass during cooling. For a cooling. rate of about 1 Q. per minute, the setting point temperature for the madority of ordinary glasses is approximately 20 C. below the annealing temperature of the glass. ,In order for a glass to seal successfully to a. metal, the overall contrasttion of the glass between its setting point tern-- perature and roomtemperature must be substantiallythe same as that of the metal between the same temperatures. In other words, the expansion curves of the glass and the metal must intersect. at these temperatures. This qualification is characteristic of the new glasses and Fernico.

I I have found that. the overall elongation of Fernico between room temperature and 460 C. is the same as that of molybdenum, that is, their expansion curves intersect at this point. This elongation amounts to 239x parts perunit length. An. important advantage of my new glasses resides in the fact that their setting point temperatures are sufl'iciently close to 460 C;. that they can'besealedequally well either to Femico'? or to molybdenum. a

m order to illustrate the relationship between. l

mately 67% SiOz,

1320s,. about. 7.5%

matelw 674757;. 8192., 1546-7, Brat, about 1.5%.- .andabout-1%. Lia and about 3% 39.0. the electrtcal resistivity at 350 (1; being. over nine mcgohms per cm. cube and. the setting point temperature of the Elass, being. about-460 C..and .its.speciflc elongation be.- tween C. and- 460 C. being. about. 25x11? unitlength. i

1. A. glass or high electrical. resistivity and chemical. durability which. consists of. approx-1'- B203, 7.5% Mamw 2. 5%. NaaQ,,s3.5 '7i-KzO., .6F/a-Lia0 and.3% B00. theelestrim at -350 (Lbeins over. nine mail.- ohms er om. cube. the setting, point. temperature of, the 'glass being about. 460 0.. and its. elongation between.41b C. and 460 Qheins about. 2.4x10- partsper unitilenath.

3. Aglass-ta-metai ssaLin-whichihhag'lssa consistsof approximatelw67%-Si0a 15% 3:04. 7.51% AlaOa, 2.5% NazO, 3.5% m .6-%-Lis0 and.3% B89, and; has an. electrical resistivity M1350? C. over 9 megohmsper cm. cube,,a.setting point-tentperawrev about 46.0? C... and-a. speomrr elongation between 25 C. and 460 C. ofiahout 23x10!" parts per unit. lengtm 4... AMetO IIIGtS-LSEBLYB which thsglasssons sistsof approximately 6'Z-fi'l.5% sic. LE-%.. 14% Nine, a-saa KIQ- about 1%. and about. 3%. 38.0,, and: haaan. electricak resistivity at. 350 Chosen a per cm. cu be, asetting, point. temperature. about. 460? C. and-ai spedfle eiongation betneen zfif-e. and 460 cant about parts per unit a i CERTIFICATE OF coRREcTI N. Pat nt No. '2,592,31Lg... a h Janugfy 1 M, ROBERT mmmen;

I It is hereby ee'rtiiied that the name: of the a'ssigzee in theabove numbere d patent was erroneons ly described and specified as "Corning Glaser Company" whereas said name should have been described and specified as --Corning Glass werks', Qf Corning, New York, a corporation of New York",

as shown by the rec 0rd of assignments in this Iof-fice; and that the said Letters Patent should be. read with this cflorrection therein that the same may conform to the record of the icase in the Patent Office. I

' Signed and sealedthis 19th day of March, A D. 19%,

Leslie Frazer (Seal) First Assistant Commissioner of Patents. 

